A tidal wave of toxic red mud has swept through several villages in western Hungary, engulfing everything in its path.
At least four people have died and scores more have been injured. Several peole are thought to be missing.
A state of emergency has been declared in three provinces in Western Hungary.
The sludge spill came from an overflowing reservoir near an aluminium smelting plant.
Emergency workers are pouring plaster into a nearby culvert to help neutralise the overflow.
Officials say tests show there is no acute health risk from radiation.
Amid the wreckage, people are trying to salvage what they can from their buried homes but police are not letting them back in.
Scores of people have been taken to hospital, many with burns and eye irritations due to corrosive chemicals in the sediment.
At a news conference, Hungary’s Prime Minister said there is no sign that the spill was due to natural causes.
He suggested it may have been caused by human error.
The fear is the toxic sediment will find its way into the Danube, one of Europe’s major waterways.